If he'd had access to a lot of information about what the courts would do, and if he'd been prepared to really strain himself and his credibility to carry such a measure beforehand, it still wouldn't have put the amendment through.
So, this article looks a lot like hindsight to me. You can come along afterwards and say, "at this point, he should have acted," but at the time Romney probably didn't have the information that we all have after the fact.